In the past two decades, a great deal of attention has been directed to the study of synaptogenesis in the mammalian central nervous system. Many of these studies are driven by the belief that the diagnosis and the prevention of synapse loss associated with several neurodegenerative diseases can be achieved through a better understanding of the basic mechanisms of synapse formation in central neurons. Although these mechanisms are not completely understood, it is tempting to speculate that proteins, such as agrin, that play a key role in the formation of the neuromuscular junction might also play an important role in the formation of synaptic contacts between neurons. Recently, we have shown that agrin differentially regulates the rates of axonal and dendritic elongation as well as synapse formation in hippocampal neurons. However, the agrin receptor(s) has yet to be identified in these neurons. The experiments proposed here are intended to test the following hypothesis: ror proteins, two tyrosine kinase receptors considered "orphan receptors", could mediate the effects of agrin on early stages of development in central neurons. A combination of techniques including: Western blot analysis, immunocytochemistry, RT-PCR, the generation of null mutations, binding assays, and immunoprecipitation will be used to analyze: 1) the pattern of expression and localization of ror 1 and ror 2 in central neurons; 2) the role of these tyrosine kinase receptors in neurite elongation and synapse formation; and 3) the participation of ror 1 and ror 2 in the agrin-signaling pathway.